Terminal and communication method

ABSTRACT

A DCI receiving unit receives downlink control information (DCI) indicative of allocation of an uplink (UL) signal of a first TTI (long TTI) or an uplink signal of a second TTI (sTTI) having a shorter TTI length than the first TTI; a transmission power determination unit determines transmission power of the uplink signal of the first TTI and transmission power of the uplink signal of the second TTI; and a transmitting unit transmits the uplink signal of the first TTI and the uplink signal of the second TTI by using the determined transmission power on the basis of the downlink control information. The transmission power determination unit reserves desired transmission power for the uplink signal of the second TTI in the first TTI in a case where decoding of the downlink control information indicative of allocation of the uplink signal of the second TTI to be transmitted within the first TTI (e.g., a subframe) is completed before start of transmission of the uplink signal of the first TTI.

TECHNICAL FIELD

The present disclosure relates to a terminal and a communication method.

BACKGROUND ART

In recent years, realization of an application (a delay-criticalapplication) that is required to shorten a delay time is beingconsidered. Examples of such an application that is required to shortena delay time include an application for autonomous driving, asuper-reality application for smartglasses, and an application forcommunication between apparatuses.

In the 3GPP, latency reduction for reducing packet delay is beingconsidered in order to realize such applications (see Non PatentLiterature 1). In the latency reduction, it is being considered that alength of a transmission time interval (TTI), which is a time unit fordata transmission and reception, is shortened to a length ranging from0.5 msec to 1 symbol. A conventional TTI length is 1 msec, which isequal to a unit called a subframe. A single subframe is constituted by 2slots (1 slot is 0.5 msec). A single slot is constituted by 7 symbols inthe case of normal cyclic prefix (CP) and is constituted by 6 symbols inthe case of extended CP. For example, in a case where the shortened TTIlength is 0.5 msec, 2 TTIs are provided per msec. In a case where 1 slotis divided into a TTI of 4 symbols and a TTI of 3 symbols, 4 TTIs areprovided per msec. In a case where a TTI length is 2 symbols, 7 TTIs areprovided per msec.

Shortening a TTI length can reduce delay of a channel quality indicator(CQI) report, thereby increasing frequency of a CQI report. Thisproduces an advantage of reducing a difference between a CQI report andactual line quality.

CITATION LIST Non Patent Literature

Non Patent Literature 1: RP-150465, “New SI proposal: Study on Latencyreduction techniques for LTE,” Ericsson, Huawei, March 2015

Non Patent Literature 2: 3GPP TR 36.211 V13.0.0, “Physical channels andmodulation (Release 13),” December 2015

Non Patent Literature 3: R1-164923, “Simultaneous Transmission of ULSignals for Shortened TTI Operation,” Nokia, Alcatel-Lucent ShanghaiBell, May 2016

SUMMARY OF INVENTION

For example, shortening of a TTI length can be applied not only to anenhanced Long Term Evolution (LTE) system, but also to a system realizedby a new frame format called a new radio access technology (RAT). In theNew RAT, there is a possibility that the number of symbols per msec isdifferent from that in the LTE. In a shortened TTI (hereinafter referredto as a short TTI (sTTI)) operation, plural TTI lengths may be supportedsimultaneously (see, for example, Non Patent Literature 3). In a casewhere plural TTI lengths are supported, TTI lengths can be selected andused in accordance with requests from different applications. Forexample, a long TTI can be used for a packet that permits delay, and ansTTI can be used for a packet that is strict with delay.

However, in a case where maximum transmission power that can be used fora terminal (sometimes referred to as a UE) is not sufficient,simultaneous transmission of packets using plural TTIs having differentTTI lengths undesirably causes shortage of transmission power. It istherefore necessary to consider how transmission power is distributed ina case where TTI lengths are different.

An aspect of the present disclosure provides a terminal and acommunication method that can properly set how transmission power isdistributed in a case where TTI lengths are different.

A terminal according to an aspect of the present disclosure includes areceiving unit that receives downlink control information indicative ofallocation of an uplink signal of a first transmission time interval(TTI) or an uplink signal of a second TTI having a shorter TTI lengththan the first TTI; a transmission power determination unit thatdetermines transmission power of the uplink signal of the first TTI andtransmission power of the uplink signal of the second TTI; and atransmitting unit that transmits the uplink signal of the first TTI andthe uplink signal of the second TTI by using the determined transmissionpower on a basis of the downlink control information, wherein thetransmission power determination unit reserves desired transmissionpower for the uplink signal of the second TTI in the first TTI in a casewhere decoding of the downlink control information indicative ofallocation of the uplink signal of the second TTI to be transmittedwithin the first TTI is completed before start of transmission of theuplink signal of the first TTI.

It should be noted that general or specific embodiments may beimplemented as a system, a device, a method, an integrated circuit, acomputer program, a storage medium, or any selective combinationthereof.

According to an aspect of the present disclosure, it is possible toproperly set distribution of transmission power in a case where TTIlengths are different.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a substantialpart of a terminal according to Embodiment 1.

FIG. 2 is a block diagram illustrating a configuration of a base stationaccording to Embodiment 1.

FIG. 3 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1.

FIG. 4A illustrates an example of a transmission timing according toOperation Example 1 of Embodiment 1.

FIG. 4B illustrates an example of distribution of transmission poweraccording to Operation Example 1 of Embodiment 1.

FIG. 5A illustrates an example of a transmission timing according toOperation Example 1 of Embodiment 1.

FIG. 5B illustrates an example of distribution of transmission poweraccording to Operation Example 1 of Embodiment 1.

FIG. 6 illustrates an example of a transmission timing according toOperation Example 2 of Embodiment 1.

FIG. 7 illustrates an example of a transmission timing according toOperation Example 2 of Embodiment 1.

FIG. 8 illustrates an example of a transmission timing according toOperation Example 2 of Embodiment 1.

DESCRIPTION OF EMBODIMENTS

[Background Leading to Aspect of Present Disclosure]

The background leading to an aspect of the present disclosure isdescribed below.

[Operation of Dual Connectivity]

In dual connectivity, a terminal can transmit an uplink (UL) signalsimultaneously in a plurality of cells. Each of the cells belongs to amaster cell group (MCG) or a secondary cell group (SCG), andtransmission power can be distributed by determining priorities for ULtransmission of the MCG and UL transmission of the SCG.

In dual connectivity, minimum guaranteed power is allocated to each CGas power distribution in UL transmission. In a case where a terminaluses transmission power equal to or larger than the minimum guaranteedpower, the terminal can use remaining transmission power (remainingpower) in accordance with a priority. In a method for power distributionapplied in a case where the MCG and the SCG are not synchronized,transmission power of a signal whose transmission starts earlier is notchanged.

[Premise]

As for power distribution among TTIs in a case where plural TTI lengthsare supported simultaneously, minimum guaranteed power may be allocatedto each TTI while regarding a TTI as a cell group as in the case of dualconnectivity. For example, in a case where transmission power equal toor larger than the minimum guaranteed power is needed in each TTI,remaining power may be distributed in accordance with priorities orremaining power may be allocated to a signal of a TTI whose transmissionstarts earlier.

[Problem]

In a case where UL signals of plural TTIs having different TTI lengthsare transmitted simultaneously, there is a possibility that a UL signalof an sTTI is allocated and transmission of the UL signal of the sTTIstarts after start of transmission of a UL signal of a long TTI. In sucha case, shortage of power allocated to the UL signal of the sTTIundesirably occurs in a case where remaining power is small since powerhas been already allocated to the UL signal of the long TTI even if thepriority of the UL signal of the sTTI is higher than the priority of theUL signal of the long TTI.

One measure to give a priority to an sTTI is to always reserveguaranteed power for the sTTI. In this case, however, there is a problemthat power allocated to a TTI is always small even in a case where thereis no UL allocation of the sTTI. Furthermore, according to a method inwhich priorities are not determined in accordance with TTI lengths and aUL signal whose transmission starts earlier uses remaining power,unbalance occurs, specifically, a longer TTI more frequently usesremaining power than an sTTI.

In view of the circumstances, an object of an aspect of the presentdisclosure is to properly distribute power in a case where UL signals ofdifferent TTI lengths are transmitted.

Next, embodiments of the present disclosure are described in detailbelow with reference to the drawings.

Embodiment 1

[Outline of Communication System]

A communication system according to each embodiment of the presentdisclosure includes a base station 100 and a terminal 200.

FIG. 1 is a block diagram illustrating a configuration of a substantialpart of the terminal 200 according to the embodiment of the presentdisclosure. In the terminal 200 illustrated in FIG. 1, a DCI receivingunit 207 receives downlink control information (DCI) indicative ofallocation of an uplink (UL) signal of a first TTI (a long TTI) and anuplink signal of a second TTI (sTTI) having a shorter TTI length thanthe first TTI; a transmission power determination unit 211 determinestransmission power for the uplink signal of the first TTI andtransmission power for the uplink signal of the second TTI; and atransmitting unit 212 transmits the uplink signal of the first TTI andthe uplink signal of the second TTI with the determined transmissionpower on the basis of the downlink control information. In a case wheredecoding of downlink control information indicative of allocation of theuplink signal of the second TTI to be transmitted within the first TTI(e.g., a subframe) is completed before start of transmission of theuplink signal of the first TTI, the transmission power determinationunit 211 reserves desired transmission power for the uplink signal ofthe second TTI in the first TTI.

[Configuration of Base Station]

FIG. 2 is a block diagram illustrating a configuration of the basestation 100 according to the present embodiment. In FIG. 2, the basestation 100 includes a downlink control information (DCI) generationunit 101, an error correction encoding unit 102, a modulating unit 103,a signal allocating unit 104, a transmitting unit 105, a receiving unit106, a signal separating unit 107, an ACK/NACK receiving unit 108, ademodulating unit 109, and an error correction decoding unit 110.

The DCI generating unit 101 determines which of an sTTI, a TTI, or bothof an sTTI and a TTI is used to transmit transmission data signal (DLdata signal). Furthermore, the DCI generating unit 101 determines whichof an sTTI, a TTI, or both of an sTTI and a TTI is used to receive ULdata signal. The DCI generating unit 101 determines whether or not it isnecessary to retransmit the DL data signal on the basis of contents (ACKor NACK) of an ACK/NACK signal (i.e., an ACK/NACK signal received inresponse to the DL data signal (physical downlink shared channel(PDSCH)) supplied from the ACK/NACK receiving unit 108 and generates DCIfor sTTI or DCI for TTI in accordance with a result of thedetermination. The DCI generating unit 101 supplies a control signalconcerning DL (e.g., DL resource allocation information) to the signalallocating unit 104 and supplies a control signal concerning UL (e.g.,UL resource allocation information) to the signal separating unit 107.

Furthermore, in a case where simultaneous transmission using an sTTI anda TTI occurs in a UL channel in the terminal 200, the DCI generatingunit 101 predicts a transmission power margin level (e.g., remainingpower) of the terminal 200, for example, from a power headroom anddetermines whether or not simultaneous transmission using an sTTI and aTTI is possible in the terminal 200 on the basis of the predicted marginlevel. For example, in a case where a signal of a higher priority than aTTI is allocated in an sTTI, the DCI generating unit 101 allocates thesignal to an sTTI on a front side of a subframe in order to reservetransmission power.

Furthermore, the DCI generating unit 101 performs encoding processingand modulation processing on the generated DCI and then supplies themodulated DCI to the signal allocating unit 104 in order to transmit themodulated DCI to the terminal 200.

The error correction encoding unit 102 performs error correctionencoding on transmission data signal (DL data signal) and upper layersignaling (not illustrated) and then supplies the encoded signal to themodulating unit 103.

The modulating unit 103 performs modulation processing on the signalreceived from the error correction encoding unit 102 and supplies themodulated signal to the signal allocating unit 104.

The signal allocating unit 104 allocates the signal received from themodulating unit 103 and the DCI that is a control signal received fromthe DCI generating unit 101 to a predetermined downlink resource on thebasis of the DL resource allocation information supplied from the DCIgenerating unit 101. In this way, a transmission signal is formed. Thetransmission signal thus formed is supplied to the transmitting unit105.

The transmitting unit 105 performs wireless transmission processing suchas upconversion on the transmission signal supplied from the signalallocating unit 104 and then transmits the transmission signal to theterminal 200 via an antenna.

The receiving unit 106 receives a signal transmitted from the terminal200 via an antenna, performs wireless reception processing such asdownconversion on the received signal, and then supplies the signal tothe signal separating unit 107.

The signal separating unit 107 specifies reception frequency and timingof a UL data signal and an ACK/NACK signal on the basis of the ULresource allocation information supplied from the DCI generating unit101. Then, the signal separating unit 107 separates the UL data signalfrom the received signal and then supplies the UL data signal to thedemodulating unit 109, and separates the ACK/NACK signal from thereceived signal and then supplies the ACK/NACK signal to the ACK/N ACKreceiving unit 108.

The ACK/NACK receiving unit 108 supplies, to the DCI generating unit101, contents (ACK or NACK) of the ACK/NACK signal that is received inresponse to the DL data signal and is then supplied from the signalseparating unit 107.

The demodulating unit 109 performs demodulation processing on the signalsupplied from the signal separating unit 107 and then supplies thesignal thus obtained to the error correction decoding unit 110.

The error correction decoding unit 110 decodes the signal supplied fromthe demodulating unit 109 and thus obtains a reception data signal (ULdata signal) received from the terminal 200.

[Configuration of Terminal]

FIG. 3 is a block diagram illustrating a configuration of the terminal200 according to the present embodiment. In FIG. 3, the terminal 200includes a receiving unit 201, a signal separating unit 202, ademodulating unit 203, an error correction decoding unit 204, an errordetermining unit 205, an ACK/NACK generating unit 206, a DCI receivingunit 207, an error correction encoding unit 208, a modulating unit 209,a signal allocating unit 210, a transmission power determination unit211, and a transmitting unit 212.

The receiving unit 201 receives a reception signal (for example,including DCI for sTTI or DCI for TTI) via an antenna, performsreception processing such as downconversion on the reception signal, andthen supplies the reception signal to the signal separating unit 202.

The signal separating unit 202 separates a signal placed in a resourceto which DCI may be possibly allocated and then supplies the signal tothe DCI receiving unit 207. Furthermore, the signal separating unit 202separates a DL data signal from the reception signal on the basis of DLresource allocation information supplied from the DCI receiving unit 207and then supplies the DL data signal to the demodulating unit 203.

The demodulating unit 203 demodulates the signal received from thesignal separating unit 202 and then supplies the demodulated signal tothe error correction decoding unit 204.

The error correction decoding unit 204 decodes the demodulated signalreceived from the demodulating unit 203 and outputs a reception datasignal thus obtained. Furthermore, the error correction decoding unit204 supplies the reception data signal to the error determining unit205.

The error determining unit 205 detects an error by cyclic redundancycheck of the reception data signal and then supplies a result of thedetection to the ACK/NACK generating unit 206.

The ACK/NACK generating unit 206 generates ACK in a case where no erroris detected and generates NACK in a case where an error is detected onthe basis of the result of the detection of the reception data signalthat is supplied from the error determining unit 205 and then suppliesan ACK/NACK signal thus generated to the signal allocating unit 210.

The DCI receiving unit 207 performs demodulation processing and decodingprocessing on the DCI (the DCI for TTI or the DCI for sTTI) receivedfrom the signal separating unit 202. Then, the DCI receiving unit 207supplies a control signal (e.g., DL resource allocation information)concerning DL indicated by the decoded DCI to the signal separating unit202 and supplies a control signal (e.g., UL resource allocationinformation) concerning UL to the signal allocating unit 210.

The error correction encoding unit 208 performs error correctionencoding on a transmission data signal (UL data signal) and thensupplies the data signal thus encoded to the modulating unit 209.

The modulating unit 209 modulates the data signal received from theerror correction encoding unit 208 and then supplies the modulated datasignal to the signal allocating unit 210.

The signal allocating unit 210 allocates the data signal supplied fromthe modulating unit 209 to a resource on the basis of the UL resourceallocation information received from the DCI receiving unit 207 and thensupplies the data signal to the transmission power determination unit211 and the transmitting unit 212. Furthermore, the signal allocatingunit 210 allocates the ACK/NACK signal supplied from the ACK/NACKgenerating unit 206 to a resource for ACK/NACK or multiplexes theACK/NACK signal with the UL data signal and then supplies the ACK/NACKsignal to the transmission power determination unit 211 and thetransmitting unit 212.

The transmission power determination unit 211 determines transmissionpower for the transmission signal and the ACK/NACK signal supplied fromthe signal allocating unit 210. Specifically, the transmission powerdetermination unit 211 determines transmission power for a UL signal ofa long TTI and transmission power for a UL signal for an sTTI. Forexample, in a case where transmission of the UL signal of the sTTIoccurs during transmission of the UL signal of the long TTI, thetransmission power determination unit 211 can decode resource allocationinformation indicated by DCI (DCI for sTTI) indicative of allocation ofthe UL signal (channel) of the sTTI before a timing of the start oftransmission of the long TTI that corresponds to a subframe boundary. Inaddition, in a case where a priority of the UL signal of the sTTI ishigher than a priority of the UL signal of the long TTI, thetransmission power determination unit 211 reserves transmission powerfor the UL signal of the sTTI. Meanwhile, in a case where the priorityof the UL signal allocated to the sTTI is lower than the priority of theUL signal of the long TTI, the transmission power determination unit 211prioritizes the UL signal of the TTI in reserving transmission power.The transmission power determination unit 211 supplies transmissionpower information indicative of the determined transmission power to thetransmitting unit 212.

The transmitting unit 212 sets transmission power on the basis of thetransmission power information supplied from the transmission powerdetermination unit 211 and then transmits the signal supplied from thesignal allocating unit 210 via an antenna after performing transmissionprocessing such as upconversion. In this way, the UL signal of the longTTI and the UL signal of the sTTI are transmitted with the transmissionpower determined by the transmission power determination unit 211 byusing a resource indicated by the DCI.

[Operation of Base Station 100 and Terminal 200]

Operation of the base station 100 and the terminal 200 configured asabove is described in detail below.

The following discusses an LTE system as an example. Specifically, it isassumed that a long TTI is 1 msec, which is a subframe length of LTE,and normal LTE operation is performed in the long TTI. Hereinafter, TTIshaving different TTI lengths are referred to as a long TTI (or simply asa TTI) and a short TTI (sTTI).

The following describes an example in which the terminal 200 transmits aUL signal of an sTTI given a high priority during transmission of aphysical uplink shared channel (PUSCH) or a physical uplink controlchannel (PUCCH) that is a UL signal (UL channel) of a long TTI.

In a case where it is determined before transmission of the UL signal ofthe TTI that the UL signal of the sTTI given a high priority istransmitted in a subframe identical to the UL signal of the TTI, theterminal 200 reserves transmission power for the sTTI.

The UL signal (UL channel) transmitted in the sTTI is, for example,ACK/NACK for an sPDSCH (a short PDSCH. DL data), an sPUSCH (UL data),periodic channel state information (CSI), aperiodic CSI, or an SR(scheduling request). A timing at which it is determined whether or notto reserve transmission power for the UL channel of the sTTI variesdepending on the kind of UL channel as follows.

In the case of “ACK/NACK for an sPDSCH”, the terminal 200 determineswhether or not to reserve transmission power for the UL channel(ACK/NACK) of the sTTI at a timing at which decoding of downlink controlchannel (DCI) indicative of allocation of the sPDSCH is completed. TheDCI indicates that the sPDSCH is allocated to an sTTI identical to ansTTI to which the DCI is allocated. Then, the terminal 200 transmitsACK/NACK in a UL sTTI after K TTIs (K is an integer) from reception ofthe sPDSCH. Therefore, the terminal 200 can determine that ACK/NACK istransmitted after K TTIs from reception of the DCI, at the timing ofcompletion of decoding of the DCI even in a case where decoding of thesPDSCH has not been completed. That is, the terminal 200 can determinewhether or not to reserve transmission power for ACK/NACK for the sPDSCHallocated by the DCI at the timing of completion of decoding of the DCI.

In the case of “sPUSCH”, the terminal 200 determines whether or not toreserve transmission power for the UL channel (sPUSCH) of the sTTI at atiming at which decoding of DCI indicative of allocation of the sPUSCHis completed. The DCI indicates that the sPUSCH is allocated to a ULsTTI that is K TTIs later than the DCI. Therefore, the terminal 200 candetermine that the sPUSCH is transmitted after K TTIs from reception ofthe DCI, at the timing of completion of decoding of the DCI. That is,the terminal 200 can determine whether or not to reserve transmissionpower for the sPUSCH allocated by the DCI at the timing of completion ofdecoding of the DCI.

In the case of “aperiodic CS I”, the terminal 200 determines whether ornot to reserve transmission power for the UL channel (aperiodic CSI) ofthe sTTI at a timing at which decoding of DCI indicative of allocationof the aperiodic CSI is completed. As in the case of the sPUSCH, the DCIindicates that the CSI is allocated to an sTTI that is K TTIs later thanthe DCI. Therefore, the terminal 200 can determine that the aperiodicCSI is transmitted after K TTIs from reception of the DCI at the timingof completion of decoding of the DCI. That is, the terminal 200 candetermine whether or not to reserve transmission power for the aperiodicCSI allocated by the DCI at the timing of completion of decoding of theDCI.

Details of distribution of transmission power in the cases of ACK/NACKfor an sPDSCH, an sPUSCH, and aperiodic CSI, i.e., distribution oftransmission power for a UL channel indicated by DCI will be describedlater. In LTE/LTE-Advanced, K is 4 or more, but a different value may beused as for an sTTI.

In the case of the “periodic CSI”, the terminal 200 determines whetheror not to reserve transmission power for a UL channel (periodic CSI) ofan sTTI at a timing at which decoding of upper layer signaling thatallocates the periodic CSI is completed. Periodic transmission of theperiodic CSI is indicated by the upper layer signaling. Therefore, theterminal 200 recognizes in advance in which subframe the CSI of the sTTIis transmitted. Accordingly, the terminal 200 reserves transmissionpower for the CSI of the sTTI in a case where a priority of the CSI ofthe sTTI is higher than a priority of the UL signal of the long TTI anddoes not reserve transmission power for the CSI of the sTTI in a casewhere the priority of the CSI of the sTTI is lower than the priority ofthe UL signal of the long TTI.

In the case of “SR”, the terminal 200 cannot determine in advancewhether or not to reserve transmission power for a UL channel (SR) of ansTTI. When an SR of an sTTI occurs during transmission of a long TTI,the terminal 200 checks transmission power (remaining power) that can beallocated to the SR. In a case where it is determined that sufficienttransmission power can be allocated to transmission of the SR, theterminal 200 transmits the SR at any timing. Meanwhile, in a case whereit is determined that sufficient transmission power cannot be allocatedto transmission of the SR, the terminal 200 transmits the SR afterwaiting until the SR becomes transmittable in a next subframe orthereafter. Note, however, that in a case where transmission power hasbeen already reserved for a UL signal (a UL signal other than the SR) ofan sTTI, the terminal 200 may allocate the transmission power reservedin advance in a subframe to an SR occurring in the subframe.

Distribution of transmission power for a UL channel (ACK/NACK for ansPDSCH, an sPUSCH, or aperiodic CSI) allocated by an sPDCCH (DCI) isdescribed in detail below.

Operation Example 1

FIGS. 4A and 5A illustrate an example of a timing of an sTTI PDCCH (DCI)indicative of allocation of a UL signal (e.g., ACK/NACK for an sPDSCH,an sPUSCH, or aperiodic CSI) of an sTTI and a timing of the UL signal(sTTI sPUSCH/sPUCCH). FIGS. 4B and 5B illustrate an example ofdistribution of transmission power to a UL signal of an sTTI and a ULsignal of a long TTI in a subframe #1 of FIGS. 4A and 5A in the terminal200.

In FIGS. 4A and 5A, a short TTI (sTTI) is constituted by 2 symbols (i.e.7 sTTIs per ms (TTI)) in both DL and UL.

It is assumed that a sum of desired transmission power for the UL signalof the sTTI and desired transmission power for the UL signal of the TTIexceeds maximum transmission power (Pmax) of the terminal 200.

The DCI is allocated to 2 symbols (i.e., 1 sTTI) of DL. Furthermore, aninterval between the DCI and a UL signal allocated by the DCI is K=4.That is, the UL signal allocated by the DCI is transmitted after 4 sTTIsfrom transmission of the DCI.

Furthermore, it is assumed that a processing time needed for decoding ofthe DCI and adjustment of transmission power of the UL signal in theterminal 200 is 2 symbols.

In FIG. 4A, the UL signal is allocated to an sTTI #2 of the subframe #1.This UL signal is allocated by an sPDCCH that is transmitted 4 sTTIsearlier, i.e., DCI transmitted in a sixth sTTI (sTTI #5) of the subframe#0.

The terminal 200 decodes the DCI received in the sTTI #5 of the subframe#0 within 2 symbols. That is, the terminal 200 completes decoding in ansTTI #6 of a subframe #0 followed by the subframe #1. Then, in a casewhere a UL signal of an sTTI given a high priority is allocated by thedecoded DCI, the terminal 200 reserves transmission power for the sTTIand starts transmission of a UL signal of a long TTI in the subframe #1by using remaining transmission power other than the reservedtransmission power.

That is, the terminal 200 reserves desired transmission power fortransmission of the UL signal of the sTTI in the sTTI #2 of the subframe#1 as illustrated in FIG. 4B at a timing of completion of decoding ofthe DCI in the subframe #0 before start of the subframe #1 anddistributes remaining transmission power to the UL signal (TTIPUSCH/PUCCH) of the long TTI transmitted in the subframe #1. This allowsthe terminal 200 to transmit the UL signal of the sTTI in the sTTI #2 ofthe subframe #1 by utilizing the reserved transmission power.

Meanwhile, in FIG. 5A, a UL signal is allocated to an sTTI #3 of thesubframe #1. This UL signal is allocated by an sPDCCH that istransmitted 4 sTTIs earlier, i.e., DCI transmitted in a seventh sTTI(sTTI #6) of the subframe #0.

The terminal 200 decodes the DCI received in the sTTI #6 of the subframe#0 within 2 symbols. However, as illustrated in FIG. 5A, the terminal200 decodes the DCI in a section of the subframe #1. That is, theterminal 200 does not complete decoding of the DCI concerning an sTTIbefore a timing at which transmission power of the UL signal of the TTIis changeable, i.e., before start of the subframe #1.

In view of this, the terminal 200 starts transmission of the UL signalof the long TTI of the subframe #1 by using desired transmission powerwithout waiting for decoding of the DCI of the sTTI. That is, theterminal 200 does not reserve desired transmission power fortransmission of the UL signal of the sTTI in the sTTI #3 of the subframe#1 at a timing of start of the subframe #1. Therefore, as illustrated inFIG. 5B, the terminal 200 transmits, in the sTTI #3 of the subframe #1,the UL signal of the sTTI by using remaining transmission power otherthan the transmission power used for the UL signal of the long TTI evenin a case where a priority of the UL signal of the sTTI is high.

That is, in the example illustrated in FIGS. 4A and 5A, in a case whereDCI indicative of allocation of a UL signal given a high priority isallocated between sTTI #0 and sTTI #2 in the subframe #1, the terminal200 can complete decoding of the DCI corresponding to the UL signal(i.e., specifies allocation of the UL signal of the sTTI) before startof the subframe #1 and reserve desired transmission power for the ULsignal in advance. This allows the terminal 200 to transmit the ULsignal of the sTTI given a high priority with sufficient transmissionpower even during transmission of the UL signal of the TTI.

Meanwhile, in the example illustrated in FIGS. 4A and 5A, in a casewhere DCI indicative of allocation of the UL signal is allocated betweensTTI #3 and sTTI #6 in the subframe #1, decoding of the DCI is notcompleted before start of the subframe #1. Therefore, even in a casewhere DCI indicative of allocation of a UL signal given a high priorityis received between sTTI #3 and sTTI #6 of the subframe #1, the terminal200 transmits a UL signal of a long TTI transmitted in the subframe #1by using desired transmission power without reserving desiredtransmission power for transmission of the UL signal given a highpriority.

Furthermore, as illustrated in FIG. 5B, the terminal 200 keepstransmission power for UL transmission in the long TTI at a constantlevel within the same subframe (subframe #1) after start of transmissionof the UL signal of the long TTI. In a case where multilevel modulation(16QAM, 64QAM, 256QAM) that uses an amplitude is used as a modulationmethod, there occurs a problem that a change of transmission power of asignal in the middle of transmission of the signal causes a differencein power between a reference signal (demodulation reference signal(DMRS)) and reception data in the base station 100, thereby preventingthe reception data from being correctly demodulated. Therefore, qualityof channel estimation can be maintained in the case of multilevelmodulation by keeping transmission power of the UL signal of the longTTI at a constant level. Furthermore, in a case where a PUCCH istransmitted from the terminal 200 and transmission power is determinedby the base station 100, power of the PUCCH is easily detected in thebase station 100 by keeping transmission power of the UL signal of thelong TTI at a constant level.

Operation Example 2

In Operation Example 2, a time difference between DL and UL isconsidered in addition to the operation described in Operation Example1.

Specifically, as for an actual UL frame timing, a UL transmission timingis shifted forward by an instruction of Timing Advance (TA) while usinga DL frame reception timing of a UE as a reference although a timedifference between DL and UL is not illustrated in Operation Example 1(FIGS. 4A and 5A). TA is a value for adjustment that allows UL signalstransmitted from a plurality of UEs to be synchronized with each otherin a base station. A distance (i.e., propagation delay) from a basestation varies from one UE to another. In general, an absolute value ofTA becomes larger as propagation delay between a base station and a UEbecomes longer, and the TA value becomes closer to 0 as the propagationdelay becomes shorter.

That is, an sTTI in which transmission power for a UL signal of an sTTIcan be reserved (i.e., a timing at which it is determined whether or notto reserve transmission power for the sTTI) changes in accordance with aTA value. In view of this, in Operation Example 2, the terminal 200determines whether or not to reserve transmission power for a UL signaltransmitted in an sTTI of UL in accordance with a TA value.

In LTE/LTE-Advanced, TA is defined so that N_(TA) is equal to or largerthan 0 and is equal to or smaller than 20512, and a UL transmissiontiming is shifted forward by (N_(TA) N_(TA offset))×T_(s) seconds.

In the case of frequency division duplex (FDD), N_(TA) offset=0, and inthe case of TDD (Time Division Duplex), N_(TA) offset is 624. T_(s) is1/(15000*2048), and a length of an initial symbol within a slot is 2208T_(s) seconds and a length of a remaining symbol is 2192 T_(s) secondsin the case of Normal CP.

An example of a UL transmission timing taking TA into consideration isdescribed below with reference to FIGS. 6 through 8.

In FIGS. 6 through 8, DCI is allocated to 2 symbols of DL (i.e., 1sTTI). In FIGS. 6 through 8, it is assumed that a processing timenecessary for decoding of the DCI and adjustment of transmission powerof a UL signal in the terminal 200 is 2 symbols.

FIG. 6 illustrates UL transmission timings in a case where an sTTIlength is 2 symbols (i.e., 7 sTTIs per ms (TTI)) both in DL and UL.

FIG. 6 illustrates UL transmission timings in cases where TA is 0, TA is2192×2 (corresponding to 2 symbols), and TA is 2192×4 (corresponding to4 symbols).

First, the case where TA is 0 illustrated in FIG. 6 (i.e., a timingsimilar to FIGS. 4A and 5A) is described. In this case, in a case whereDCI is allocated to a DL sTTI #5 or earlier (any of sTTIs #3 through #5)of a subframe #0, the terminal 200 can complete decoding of the DCIbefore start of a subframe #1 and reserve transmission power for an sTTIwithin the subframe #1. That is, in the case where TA is 0 illustratedin FIG. 6, the terminal 200 can reserve transmission power for an sTTIin advance in a case where a UL signal of an sTTI is transmitted in anyof UL sTTIs #0 through #2 of the subframe #1.

Next, the case where TA is 2192×2 (corresponding to 2 symbols)illustrated in FIG. 6 is described. In this case, in a case where DCI isallocated to a DL sTTI #4 or earlier (any of sTTIs #3 and #4) of thesubframe #0, the terminal 200 can complete decoding of the DCI beforestart of the subframe #1 and reserve transmission power for an sTTIwithin the subframe #1. That is, in a case where TA is 2192×20illustrated in FIG. 6, the terminal 200 can reserve transmission powerfor an sTTI in advance in a case where a UL signal of an sTTI istransmitted in any of UL sTTIs #0 and #1 of the subframe #1.Accordingly, in the case where TA is 2192×2, the number of sTTIs forwhich transmission power can be reserved is smaller by 1 sTTI than thecase where TA is 0.

Similarly, in a case where TA is 2192×4 (corresponding to 4 symbols)illustrated in FIG. 6, the terminal 200 can reserve transmission powerfor an sTTI in an UL sTTI #0 of the subframe #1.

FIG. 7 illustrates UL transmission timings in a case where an sTTIlength of DL is 2 symbols (i.e., 7 sTTIs per ms (TTI)) and an sTTIlength of UL is 3/4 symbols (i.e., 4 sTTIs per ms (TTI)).

FIG. 7 illustrates UL transmission timings in cases where TA is 0, TA is2192×2 (corresponding to 2 symbols), and TA is 2192×4 (corresponding to4 symbols).

In FIG. 7, it is assumed that a transmission timing of DCI is based on aDL sTTI. Specifically, it is assumed that DCI is transmitted 4 DL sTTIsearlier than a transmission timing of a UL signal in a UL sTTI. Forexample, allocation of a UL sTTI #0 of the subframe #1 is indicated byDCI transmitted in a DL sTTI #3 of the subframe #0.

First, the case where TA is 0 illustrated in FIG. 7 is described. Inthis case, in a case where DCI is allocated to a DL sTTI #5 or earlier(sTTI #3 or sTTI #5) of the subframe #0, the terminal 200 can completedecoding of the DCI before start of the subframe #1 and reservetransmission power for an sTTI within the subframe #1. That is, in thecase where TA is 0 illustrated in FIG. 7, the terminal 200 can reservetransmission power for an sTTI in advance in a case where a UL signal ofan sTTI is transmitted in UL sTTI #0 or #1 of the subframe #1.

Next, the case where TA is 2192×2 (corresponding to 2 symbols)illustrated in FIG. 7 is described. In this case, in a case where DCI isallocated to a DL sTTI #4 or earlier (sTI #3) of the subframe #0, theterminal 200 can complete decoding of the DCI before start of thesubframe #1 and reserve transmission power for an sTTI within thesubframe #1. That is, in the case where TA is 2192×20 illustrated inFIG. 7, the terminal 200 can reserve transmission power for an sTTI inadvance in a case where a UL signal of an sTTI is transmitted in a ULsTTI #0 of the subframe #1. That is, in the case where TA is 2192×2, thenumber of sTTIs for which transmission power can be reserved is smallerby 1 sTTI than the case where TA is 0.

Similarly, in the case where TA is 2192×4 (corresponding to 4 symbols)illustrated in FIG. 7, the terminal 200 can reserve transmission powerfor an sTTI in a UL sTTI #0 of the subframe #1.

FIG. 8 illustrates UL transmission timings in cases where an sTTI lengthof DL is 1 slot (i.e., 2 sTTIs per ms (TTI)) and an sTTI length of UL is3/4 symbols (i.e., 4 sTTIs per ms (TTI)).

FIG. 8 illustrates UL transmission timings in cases where TA is 0, TA is2192×2 (corresponding to 2 symbols), TA is 2192×4 (corresponding to 4symbols), and TA is 2192×6 (corresponding to 6 symbols).

In FIG. 8, it is assumed that a transmission timing of DCI is based on aUL sTTI. Specifically, it is assumed that DCI is transmitted 4 UL sTTIsearlier than a transmission timing of a UL signal in a UL sTTI. Forexample, allocation of UL sTTIs #0 and #1 of a subframe #1 is indicatedby DCI transmitted in a DL sTTI #0 of a subframe #0, and allocation ofUL sTTIs #2 and #3 of the subframe #1 is indicated by DCI transmitted ina DL sTTI #1 of the subframe #0. As illustrated in FIG. 8, DCI istransmitted in 2 symbols on a front side (e.g., a part corresponding toa PDCCH) of each sTTI (1 slot length).

First, the cases where TA is 0 and TA is 2192×2 illustrated in FIG. 8are described. In these cases, in a case where DCI concerning UL usingthe subframe #1 is allocated by a timing that is 2 symbols earlier thana subframe boundary of UL, the terminal 200 can complete decoding of theDCI before start of the subframe #1 and reserve transmission power foran sTTI within the subframe #1. That is, in the cases where TA is 0 andTA is 2192×2 illustrated in FIG. 8, the terminal 200 can reservetransmission power for an sTTI in advance in a case where a UL signal ofan sTTI is transmitted in any of UL sTTIs #0 through #3 (i.e., allsTTIs) of the subframe #1.

Next, the cases where TA is 2192×4 and TA is 2192×6 illustrated in FIG.8 are described. In these cases, in a case where DCI concerning UL usingthe subframe #1 is allocated by a timing that is 2 symbols earlier thana subframe boundary of UL, the terminal 200 can complete decoding of theDCI before start of the subframe #1 and reserve transmission power foran sTTI within the subframe #1. That is, in the cases where TA is 2192×4and TA is 2192×6 illustrated in FIG. 8, the terminal 200 can reservetransmission power for an sTTI in advance in a case where a UL signal ofan sTTI is transmitted in a UL sTTI #0 or #1 of the subframe #1.

As illustrated in FIGS. 6 through 8, a UL transmission timing shiftsforward as TA becomes longer. Accordingly, a period from reception ofDCI in the terminal 200 to start of a next subframe becomes shorter, andthe number of sTTIs for which UL transmission power can be reservedbecomes smaller. As illustrated in FIGS. 6 through 8, a possibility ofreserving transmission power is higher in an earlier sTTI among aplurality of sTTIs of a subframe even in a case where TA is long.

In view of this, for example, the base station 100 may allocate, to anearlier sTTI in each subframe, DCI (DCI for an sTTI) indicative ofallocation of a UL signal of a high priority transmitted in an sTTI inthe terminal 200. This allows the terminal 200 to complete demodulationof DCI before start of a subframe in which a UL signal whose allocationis indicated by the DCI is to be transmitted, thereby increasing apossibility of reserving desired transmission power for the UL signal ofa high priority.

In the above description, a period needed to decode DCI is 2 symbols.However, a period (symbol length) needed to decode DCI is not limited to2 symbols and may be 1 symbol or may be 3 or more symbols.

A period needed to decode DCI may be defined not by the number ofsymbols but by the number of sTTIs or a period of time (second).

The following describes a method for defining, by using the number ofsymbols, the number of sTTIs, or a period of time, a criterion value fordetermining how earlier than a subframe boundary of DL allocation needbe indicated by DCI in order that the terminal 200 can reservetransmission power for a UL signal of an sTTI.

For example, the terminal 200 can decide transmission power for a ULsignal of an sTTI on the basis of the criterion value for determination.Furthermore, the base station 100 can specify, for scheduling,transmission power for a UL signal transmitted from the terminal 200 onthe basis of the criterion value for determination.

[Case of the Number of Symbols]

A case where the criterion value for determination is defined by thenumber of symbols as illustrated in FIGS. 6 through 8 is described.

The criterion value (the number of symbols) for determining by how manysymbols earlier than a DL subframe boundary allocation needed beindicated by DCI in order to reserve transmission power for a UL signalof an sTTI can be defined as shown in Table 1.

TABLE 1 The number of symbols (N_(TA) + N_(TA offset)) is equal to orsmaller than N 624 (N_(TA) + N_(TA offset)) is equal to or smaller thanN + 1 2192 + 624 and is larger than 624 (N_(TA) + N_(TA offset)) isequal to or smaller than N + 1 + X (X is 1 to 5) 2192 * (X + 1) + 624and is larger than 2192 * X + 624 (N_(TA) + N_(TA offset)) is equal toor smaller than N + 7 (2192 * 7 + 16) + 624 and is larger than 2192 *6 + 624 (N_(TA) + N_(TA offset)) is equal to or smaller than N + 1 + X(X is 7 or 8) (2129 * (X + 1) + 16) + 624 and is larger than 2192 * X +16 + 624 (N_(TA) + N_(TA offset)) is equal to or smaller than N + 1020512 + 624 and is larger than 2192 * 9 + 16 + 624

N is the number of symbols needed to decode DCI, i.e., a minimum numberof symbols (e.g., N is 2 symbols in FIGS. 6 through 8) used as thecriterion value for determination. The criterion value for determinationis the minimum number of symbols N in a case where TA is equal to orsmaller than 624 in order to encompass a case where the minimum numberof symbols N is used in TDD. That is, in Table 1, a period of time(N-symbol length−624 T_(s)) is reserved for decoding processing on theterminal 200 side.

The criterion value for determination can be determined irrespective ofa TTI length of an sTTI in a case where the criterion value fordetermination is defined by the number of symbols. Therefore, the basestation 100 and the terminal 200 can determine whether or not to reservetransmission power for an sTTI irrespective of change of setting of ansTTI on the basis of the criterion value for determination. However,there is a possibility that the minimum value N (the number of symbols)used as the criterion value for determination varies depending on ansTTI length.

[Case of the Number of sTTIs]

A case where the criterion value for determination is defined by thenumber of sTTIs of DL.

The criterion value (the number of sTTIs) for determining by how manysTTIs earlier than a subframe boundary allocation need be indicated byDCI in order to reserve transmission power for a UL signal of an sTTIcan be determined as shown in Table 2. In Table 2, it is assumed that aTTI length of a DL sTTI is 2 symbols (see, for example, FIGS. 6 and 7)and a period needed to decode DCI is 1 sTTI or more (i.e., N=1sTTI).

TABLE 2 The number of sTTIs (N_(TA) + N_(TA offset)) is equal to orsmaller than N 624 (N_(TA) + N_(TA offset)) is equal to or smaller thanN + 1 2192 * 2 + 624 and is larger than 624 (N_(TA) + N_(TA offset)) isequal to or smaller than N + 2 2192 * 4 + 624 and is larger than 2192 *2 + 624 (N_(TA) + N_(TA offset)) is equal to or smaller than N + 32192 * 6 + 624 and is larger than 2192 * 4 + 624 (N_(TA) +N_(TA offset)) is equal to or smaller than N + 4 2129 * 8 + 16 + 624 andis larger than 2192 * 6 + 624 (N_(TA) + N_(TA offset)) is equal to orsmaller than N + 5 20512 + 624 and is larger than 2192 * 8 + 624

In a case where a TTI length of a DL sTTI is 1 slot (see, for example,FIG. 8), the number of sTTIs that is the criterion value fordetermination is the minimum value N in a case where TA is equal to orless than Y as shown in Table 3. In Table 3, Y is a value that satisfies(0.5 ms*N(sTTI)−DCI length−YTS), which is a minimum period needed todecode DCI.

TABLE 3 sTTI (N_(TA) + N_(TA offset)) is equal to or smaller than Y N(N_(TA) + N_(TA offset)) is equal to or smaller than 2192 * 7 + 16 + N +1 Y and is larger than Y (N_(TA) + N_(TA offset)) is equal to or smallerthan 20512 + 624 and N + 2 is larger than 2192 * 7 + 16 + Y

[Case of Period of Time (Second)]

A case where the criterion value for determination is defined by aperiod of time.

The criterion value (period of time (second) for determining by how manyseconds earlier than a subframe boundary allocation needed be indicatedby DCI in order to reserve transmission power for a UL signal of an sTTIis defined as follows:

(N _(TA) +N _(TA) offset)T _(s) +Z[second]

Note that Z is a period of time needed to decode DCI. That is, in a casewhere DCI is received ((N_(TA) N_(TA) offset)T_(s) Z) or more earlier,the terminal 200 can decode DCI before a subframe boundary and thereforecan reserve transmission power for a UL signal of an sTTI.

However, as TA becomes longer, not only the period needed to decode DCI,but also a period for decoding of an sPDSCH and a period that can beused for generation of an sPUSCH also become shorter. Therefore, in acase where an sTTI length is shortened and an interval between DCI and aUL channel becomes shorter accordingly, there is a possibility thatdecoding of an sPDSCH and generation of an sPUSCH are not completed intime in a case where a TA length is long. Therefore, in a case where ansTTI length is shortened, a maximum value of a TA length may beshortened.

As described above, the base station 100 and the terminal 200 candetermine whether or not transmission power for a UL signal can bereserved for which sTTI of a subframe by using a TA value and thecriterion value for determination (the number of symbols, the number ofsTTIs, or a period of time). This allows the base station 100 and theterminal 200 to have common recognition concerning adjustment oftransmission power. Therefore, the base station 100 can specify, forefficient scheduling, for which sTTI transmission power can be reserved.

Operation Example 3

In a case where a plurality of UL signals of sTTIs are allocated withinthe same subframe, the terminal 200 determines reserved transmissionpower on the basis of a UL signal for which desired transmission poweris highest among UL signals of sTTIs given a higher priority than a ULsignal of a TTI transmitted simultaneously in the same subframe.

Transmission power to be reserved varies depending on a kind of ULsignal (channel) or a resource amount (the number of RBs) needed fortransmission.

Note that the terminal 200 also transmits a UL signal of an sTTI given alower priority than the UL signal of the TTI transmitted simultaneouslywithin the same subframe among the UL signals of the sTTIs by usingremaining transmission power in a case where transmission power has beenalready reserved for another UL signal of an sTTT transmitted in thesame subframe (i.e., in a case where there is unused transmissionpower).

Furthermore, the terminal 200 reserves transmission power for an sTTI ina case where a UL signal given a high priority is allocated to an earlysTTI within a subframe. In this case, the terminal 200 can transmit ansTTI allocated to a later part of a subframe by using the reservedtransmission power.

The terminal 200 can thus effectively use transmission power reservedfor a UL channel of an sTTI.

Operation Examples 1 through 3 have been described above.

As described above, in the present embodiment, in a case where decodingof DCI indicative of allocation of a UL signal of an sTTI transmittedwithin a long TTI (subframe) is completed before start of transmissionof a UL signal of the long TTI, the terminal 200 reserves desiredtransmission power for the UL signal of the sTTI in the long TTI(subframe). Furthermore, in a case where a priority of the channel ofthe sTTI is higher than a priority of the long TTI, the terminal 200reserves transmission power for transmission of the channel of the sTTI.This makes it possible to reserve sufficient transmission power for a ULsignal of an sTTI given a high priority even in the middle oftransmission of a UL signal of a long TTI. In a case where transmissionpower for a channel of an sTTI cannot be reserved, the terminal 200 canallocate sufficient transmission power for a UL signal of a long TTI.

According to the present embodiment, it is therefore possible toproperly set distribution of transmission power in a case where TTIlengths are different.

In the present embodiment, in a case where an sPUCSH or an sPDSCH of ansTTI is allocated by semi persistent schedule (SPS), the terminal 200can specify in advance whether or not a UL signal of an sTTI is to betransmitted. Therefore, in a case where SPS is applied, the terminal 200may reserve transmission power for a UL sTTI without waiting fordecoding of DCI. Even in a case where a UL signal is allocated to a latesTTI of a subframe, the terminal 200 can thus reserve transmission powerfor the UL sTT as long as a priority of the UL signal of the sTTI ishigh.

In the present embodiment, a period needed to decode DCI sometimesvaries from one terminal 200 to another. In this case, a period neededto decode DCI may be determined on the basis of capability (UEcapability) of the terminal 200. In a case where a period needed todecode DCI in the terminal 200 is unknown in the base station 100, theterminal 200 may determine from which sTTI transmission power can bereserved in accordance with capability of the terminal 200.

Embodiment 2

A base station and a terminal according to the present embodiment sharea basic configuration with the base station 100 and the terminal 200according to Embodiment 1 and are therefore described with reference toFIGS. 2 and 3.

In the present embodiment, a case where the terminal 200 determineswhether or not transmission power is reserved for an sTTI on the basisof a priority of a UL signal is described in detail.

[Operation of Dual Connectivity]

In dual connectivity, transmission power can be distributed bydetermining priorities for UL transmission of an MCG and UL transmissionof an SCG. Each cell group (CG) includes a single primary cell (PCell)or primary scell (PScell) and 0, 1, or a plurality of secondary cells(SCells). In dual connectivity, a random access channel (RACH)transmitted in the Pcell of the MCG is given a highest priority, andpriorities are allocated to respective channels as follows:

RACH>HARQ-ACK=SR>CSI>PUSCH without UCI

In a case where the same channel is transmitted in the MCG and the SCG,UL transmission of the MCG is given a higher priority than ULtransmission of the SCG.

The RACH is given a high priority because the RACH is informationnecessary for connection for communication or synchronous capture. TheHARQ-ACK is given a high priority because there is a possibility that anerror reception causes unnecessary HARQ retransmission of DL data orcauses retransmission in an upper layer without HARQ retransmission evenin a case where retransmission is necessary.

Furthermore, since it is predicted that a data amount in DL is largerthan a data amount in UL, it is desirable that the HARQ-ACK (uplinkresponse signal) is given a higher priority than UL data (physicaluplink shared channel (PUSCH)) in order to prioritize DL data.

The PUSCH without UCI (Uplink Control Information) is given a lowpriority since UL data need just be retransmitted in a case where ULdata reception quality deteriorates and influence on a system is notlarge.

In dual connectivity, there is no close cooperation between the MCG andthe SCG, and an MCG bearer and an SCG bearer are different in somecases. In this case, the MCG and the SCG may be selected and used inaccordance with priorities of applications or packets. Accordingly, anSR is separately transmitted in the MCG and the SCG, and therefore an SRand another UL signal are sometimes transmitted simultaneously even in acase where transmission power is tight. For this reason, the SR is givena high priority equal to the HARQ-ACK.

In the present disclosure, a method for distributing power among TTIswhile regarding each TTI as a cell group in dual connectivity in a casewhere a plurality of TTI lengths are supported simultaneously isdescribed. In a case where a UL signal of an sTTI and a UL signal of aTTI are simultaneously transmitted in the same component carrier (CG), ascheduler of a base station may use the sTTI or the TTI freely iftransmission power is tight. In this case, in a case where a UEtransmits an SR in an sTTI or a TTI, the base station performsscheduling of the UE so as to allocate data to an sTTI, an TTI, or bothan sTTI and a TTI.

Such operation can prevent the UE from transmitting an SR simultaneouslyin an sTTI and a TTI. Furthermore, since the signals are transmittedsimultaneously within the same CC, in a case where HARQ-ACK of a TTI oran sTTI and an SR occur simultaneously, the UE can transmit the HARQ-ACKand the SR simultaneously by changing a transmission position of a PUCCHor an sPUCCH used for transmission of the HARQ-ACK to a transmissionposition of the SR.

Furthermore, in a case where UL data is transmitted, the UE cantransmit, instead of the SR, a buffer status report (BSR) reporting abuffer state of the UE as MAC layer information in an sPUSCH of an sTTIor a PUSCH of a TTI.

The UE transmits information on the SR by selecting a method that cankeep quality of the SR on the basis of transmission power allocated toeach channel among these methods. However, in a case where quality ofthe SR cannot be kept by any of the methods since transmission power istight because of simultaneous transmission of a UL signal of an sTTI anda UL signal of a TTI, the UE transmits the SR in a later subframe. Thisprevents the UE from transmitting a low-quality SR, thereby improvingreliability of the SR. Furthermore, it is possible to keep quality ofother channels from decreasing due to interruption of an SR.

As described above, a priority of the SR can be made lower than apriority of the HARQ-ACK in the case of simultaneous transmission of ansTTI and a TTI. Priorities of the UL channels in this case can be set asfollows:

RACH>HARQ-ACK>SR>CSI>PUSCH without UCI

The CSI is a report of line quality. In dual connectivity, the CSI isgiven a higher priority than the PUSCH without UCI. However, in a casewhere a UL signal of an sTTI and a UL signal of a TTI are simultaneouslytransmitted in the same CC, the CSI can be shared by the sTTI and theTTI. The sTTI can increase frequency of transmission of the CSI sincethe number of TTIs per time becomes larger. This allows a base stationto make modification by using CSI transmitted next even in a case wherethe base station cannot correctly receive CSI.

In view of this, a priority of the UL data (PUSCH) can be made higherthan a priority of the CSI.

In this case priorities of the UL channels can be set as follows:

RACH>HARQ-ACK>SR>PUSCH with CSI>PUSCH without UCI>CSI on PUCCH

In a case where a UL signal of an sTTI and a UL signal of a TTI aresimultaneously transmitted in the same CC, influence on the TTI islarger if retransmission occurs due to deterioration of line quality.This is because a resource used for retransmission in the TTI is largerthan that in the sTTI.

In view of this, a TTI may be prioritized in simultaneous transmissionof an sTTI and a TTI. Furthermore, in a case where an sTTI is being usedbut is switched to a TTI due to deterioration of a line qualitysituation, it is preferable that the TTI is prioritized. However, it ispreferable that an sTTI is prioritized in a case where a packet forwhich low delay is requested (a packet for which a delay time should beshortened) is transmitted in an sTTI and a packet for which delay ispermitted is transmitted in a TTI.

Priorities of respective TTI lengths of a plurality of TT's havingdifferent TTI lengths may be determined in advance in a system or a basestation may notify a terminal about a TTI having a TTI length that isprioritized.

It is also possible to set priorities in accordance with kinds ofchannels and then set, for each channel, which of a TTI and an sTTI isprioritized in a case of channels of the same kind.

Operation Example

Priorities of UL channels are set as follows:

RACH>HARQ-ACK>SR>PUSCH with CSI>PUSCH without UCI>CSI on PUCCH

In a case where a priority of a UL signal of an sTTI transmitted withina long TTI is higher than a priority of a UL signal of the long TTI, theterminal 200 (transmission power determination unit 211) reservesdesired transmission power for the UL signal of the sTTI within the longTTI (e.g., a subframe).

In a case where a priority of a UL signal of a long TTI is identical toa priority of a UL signal of an sTTI (i.e., in a case of channels of thesame kind), the terminal 200 preferentially allocates desiredtransmission power for the UL signal of the long TTI within the long TTI(subframe).

The following describes operation of the terminal 200 in this operationexample.

(1) Case where ACK/NACK (HARQ-ACK) is Allocated to sTTI

The terminal 200 allocates transmission power preferentially to ACK/NACKtransmitted in an sPUCCH or an sPUSCH of an sTTI over a PUSCH with CSI,a PUSCH without UCI, or CSI transmitted on a PUCCH of a TTI. Forexample, according to the operation of Embodiment 1, the terminal 200reserves transmission power for an sTTI in a case where DCI indicativeof allocation of an sPDSCH can be received before a subframe boundary.Meanwhile, the terminal 200 allocates transmission power preferentiallyto a UL signal of a TTI in a case where an RACH or ACK/NACK is allocatedto the TTI (i.e., in a case of channels of the same kind).

(2) Case Where sPUSCH with CSI is Allocated to sTTI The terminal 200allocates transmission power preferentially to an sPUSCH with CSI of ansTTI over a PUSCH without UCI or CSi transmitted on a PUCCH of a TTI.For example, according to the operation of Embodiment 1, the terminal200 reserves transmission power for an sTTI in a case where DCIindicative of allocation of an sPUSCH can be received before a subframeboundary.

Meanwhile, in a case where an RACH, ACK/NACK, or a PUSCH with CSI isallocated to a TTI, the terminal 200 allocates transmission powerpreferentially to a UL signal of the TTI.

(3) Case where sPUSCH without CSI is Allocated to sTTI

The terminal 200 allocates transmission power preferentially to ansPUSCH without CSI over CSI transmitted on a PUCCH of a TTI. Forexample, according to the operation of Embodiment 1, the terminal 200reserves transmission power for an sTTI in a case where DCI indicativeof allocation of the sPUSCH can be received before a subframe boundary.Meanwhile, the terminal 200 allocates transmission power preferentiallyto a UL signal of a TTI in a case where an RACH, ACK/NACK, a PUSCH withCSI, or a PUSCH without CSI is allocated to a TTI.

As described above, according to the present embodiment, the terminal200 determines whether or not to reserve transmission power for an sTTIin accordance with priorities of UL signals (UL channels). That is, theterminal 200 reserves transmission power for transmission of an sTTIchannel in a case where a priority of the sTTI channel is higher than apriority of a long TTI. This makes it possible to reserve sufficienttransmission power for a UL signal of an sTTI given a high priority evenduring transmission of a UL signal of a long TTI. According to thepresent embodiment, it is therefore possible to properly setdistribution of transmission power in a case where TTI lengths aredifferent.

The embodiments of the present disclosure have been described above.

In the above embodiments, a case where a long TTI that is a subframe ofLTE and a short TTI that is an sTTI considered in LTE-Advanced are usedas an example of a plurality of TTIs having different TTI lengths hasbeen described. However, a plurality of TTIs having different TTIlengths are not limited to these and may be, for example, TTIs that usea long TTI and an sTTI in different RATs. The RAT is, for example,enhanced mobile broadband (eMBB), which is high-capacity communication,ultra-reliable and low latency communications (URLLC), or massivemachine-type communications (mMTC), which is inter-terminalcommunication. LTE and LTE-Advanced can also be regarded as examples ofthe RAT. Since suitable TTI lengths for respective RATs are different, aTTI length can vary from one RAT to another. Furthermore, TTI lengthscan be different in a plurality of systems in an RAT. Furthermore, aninterval of 1 msec is referred to as a subframe in the above embodimentsbut is not limited to this. In a different RAT, a different name can beused as a 1-msec interval that serves as a standard.

In the above embodiments, physically, a long TTI and an sTTI may beallocated to the same component carrier or may be allocated to differentcomponent carriers.

A system that uses a long TTI may be a system in which a sub-carrierinterval is narrow and a symbol interval is wide, and a system that usesa short TTI (sTTI) may be a system in which a sub-carrier interval iswide and a symbol interval is short. In LTE and LTE-Advanced, 1 msec isdivided into 14 symbols in a case of a 15-KHz sub-carrier interval andNormal CP. For example, in a case where a sub-carrier interval is 60kHz, a symbol length can be set short. This increases the number ofsymbols per msec. In this case, it is also easy to set a TTI lengthshort. Therefore, the above embodiments can be applied to a terminalthat uses a long TTI in a case where a sub-carrier interval is short anduses a short TTI in a case where a sub-carrier interval is wide and thattransmits signals simultaneously in a long TTI and a short TTI.

Although a case where a TTI (long TTI) is 1 ms has been described in theabove embodiments, a TTI length is not limited to this, and the aboveembodiments can be applied in a case where UL signals are transmittedsimultaneously by using TT's having different TTI lengths.

Although an example in which an aspect of the present disclosure isrealized by hardware has been described in the above embodiments, thepresent disclosure may be realized by software in cooperation withhardware.

Each functional block used in the description of the above embodimentsis typically an LSI that is an integrated circuit having an inputterminal and an output terminal. The integrated circuit may control eachfunctional block used in the description of the above embodiments andinclude an input terminal and an output terminal. The functional blocksmay be individually realized as one chip or some or all of thefunctional blocks may be integrated into one chip. The name used here isLSI, but it may also be called IC, system LSI, super LSI, or ultra LSIdepending on the degree of integration.

A method for integration is not limited to LSI, and a dedicated circuitor a general-purpose processor may be used. A field programmable gatearray (FPGA) that can be programmed after manufacturing an LSI or areconfigurable logic device that allows reconfiguration of theconnection or setup of circuit cells inside the LSI can be used.

Furthermore, if an integration technique that replaces LSI appears as aresult of progress of a semiconductor technology or appearance ofanother derivative technology, functional blocks may be integrated byusing the technique. One possibility is, for example, application of abiotechnology.

A terminal according to the present disclosure includes a receiving unitthat receives downlink control information indicative of allocation ofan uplink signal of a first transmission time interval (TTI) or anuplink signal of a second TTI having a shorter TTI length than the firstTTI; a transmission power determination unit that determinestransmission power of the uplink signal of the first TTI andtransmission power of the uplink signal of the second TTI; and atransmitting unit that transmits the uplink signal of the first TTI andthe uplink signal of the second TTI by using the determined transmissionpower on a basis of the downlink control information, wherein thetransmission power determination unit reserves desired transmissionpower for the uplink signal of the second TTI in the first TTI in a casewhere decoding of the downlink control information indicative ofallocation of the uplink signal of the second TTI to be transmittedwithin the first TTI is completed before start of transmission of theuplink signal of the first TTI.

The terminal according to the present disclosure is arranged such thatthe transmission power determination unit determines whether or not toreserve transmission power for the uplink signal of the second TTI on abasis of a value of Timing Advance (TA).

The terminal according to the present disclosure is arranged such thatin a case where transmission of a plurality of uplink signals of thesecond TTI occurs within the first TTI, the transmission powerdetermination unit allocates transmission power for the plurality ofuplink signals of the second TTI on a basis of a signal for which thedesired transmission power is highest among the plurality of uplinksignals of the second TTI.

The terminal according to the present disclosure is arranged such thatthe transmission power determination unit allocates the transmissionpower reserved for the uplink signal of the second TTI to another uplinksignal of the second TTI that occurs within the first TTI.

The terminal according to the present disclosure is arranged such thatanother uplink signal of the second TTI is a scheduling request (SR).

A terminal according to the present disclosure includes a receiving unitthat receives downlink control information indicative of allocation ofan uplink signal of a first transmission time interval (TTI) or anuplink signal of a second TTI having a shorter TTI length than the firstTTI; a transmission power determination unit that determinestransmission power of the uplink signal of the first TTI andtransmission power of the uplink signal of the second TTI; and atransmitting unit that transmits the uplink signal of the first TTI andthe uplink signal of the second TTI by using the determined transmissionpower on a basis of the downlink control information, wherein thetransmission power determination unit reserves desired transmissionpower for the uplink signal of the second TTI in the first TTI in a casewhere a priority of the uplink signal of the second TTI to betransmitted within the first TTI is higher than a priority of the uplinksignal of the first TTI.

The terminal according to the present disclosure is arranged such thatin a case where the priority of the uplink signal of the first TTI andthe priority of the uplink signal of the second TTI are identical, thetransmission power determination unit preferentially allocates desiredtransmission power to the uplink signal of the first TTI within thefirst TTI.

A communication method according to the present disclosure includesreceiving downlink control information indicative of allocation of anuplink signal of a first transmission time interval (TTI) or an uplinksignal of a second TTI having a shorter TTI length than the first TTI;determining transmission power of the uplink signal of the first TTI andtransmission power of the uplink signal of the second TTI; andtransmitting the uplink signal of the first TTI and the uplink signal ofthe second TTI by using the determined transmission power on a basis ofthe downlink control information, wherein desired transmission power forthe uplink signal of the second TTI in the first TTI is reserved in acase where decoding of the downlink control information indicative ofallocation of the uplink signal of the second TTI to be transmittedwithin the first TTI is completed before start of transmission of theuplink signal of the first TTI.

A communication method according to the present disclosure includesreceiving downlink control information indicative of allocation of anuplink signal of a first transmission time interval (TTI) or an uplinksignal of a second TTI having a shorter TTI length than the first TTI;determining transmission power of the uplink signal of the first TTI andtransmission power of the uplink signal of the second TTI; andtransmitting the uplink signal of the first TTI and the uplink signal ofthe second TTI by using the determined transmission power on a basis ofthe downlink control information, wherein desired transmission power forthe uplink signal of the second TTI in the first TTI is reserved in acase where a priority of the uplink signal of the second TTI to betransmitted within the first TTI is higher than a priority of the uplinksignal of the first TTI.

INDUSTRIAL APPLICABILITY

An aspect of the present disclosure is useful for a mobile communicationsystem.

REFERENCE SIGNS LIST

-   -   100 base station    -   101 DCI generating unit    -   102, 208 error correction encoding unit    -   103, 209 modulating unit    -   104, 210 signal allocating unit    -   105, 212 transmitting unit    -   106, 201 receiving unit    -   107, 202 signal separating unit    -   108 ACK/NACK receiving unit    -   109, 203 demodulating unit    -   110, 204 error correction decoding unit    -   200 terminal    -   205 error determining unit    -   206 ACK/NACK generating unit    -   207 DCI receiving unit    -   211 transmission power determination unit

1. A terminal comprising: circuitry, which, in operation, determines afirst transmission power of a first uplink signal for a firsttransmission time interval of a first radio access technology (RAT) anda second transmission power of a second uplink signal for a secondtransmission time interval of a second RAT, the first transmission timeinterval being longer than the second transmission time interval; and atransmitter, which, in operation, transmits the first uplink signal inthe first transmission time interval with the first transmission power,and transmits the second uplink signal in the second transmission timeinterval with the second transmission power, wherein the circuitry, inoperation, determines the first transmission power for the first uplinksignal and the second transmission power for the second uplink signal byreserving the first transmission power for the first uplink signal. 2.The terminal according to claim 1, wherein the circuitry, in operation,priorities the first transmission power for the first uplink signal overthe second transmission power for the second uplink signal.
 3. Theterminal according to claim 1, wherein the circuitry, in operation,reserves the first transmission power for the first uplink signal in acase where the first uplink signal is prioritized over the second uplinksignal.
 4. The terminal according to claim 1, wherein the secondtransmission time interval is within the first transmission timeinterval.
 5. The terminal according to claim 1, wherein the firsttransmission time interval is one subframe, and the second transmissiontime interval is shorter than one subframe.
 6. The terminal according toclaim 1, wherein the first RAT is a long term evolution (LTE), and thesecond RAT is a new RAT.
 7. The terminal according to claim 1, wherein asubcarrier spacing in the first RAT is narrower than a subcarrierspacing in the second RAT.
 8. The terminal according to claim 1, whereina subcarrier spacing in the first RAT is 15 kHz, and a subcarrierspacing in the second RAT is 60 kHz.
 9. A communication methodcomprising: determining a first transmission power of a first uplinksignal for a first transmission time interval of a first radio accesstechnology (RAT) and a second transmission power of a second uplinksignal for a second transmission time interval of a second RAT, thefirst transmission time interval being longer than the secondtransmission time interval; and transmitting the first uplink signal inthe first transmission time interval with the first transmission power,and transmits the second uplink signal in the second transmission timeinterval with the second transmission power, wherein the firsttransmission power for the first uplink signal and the secondtransmission power for the second uplink signal are determined byreserving the first transmission power for the first uplink signal. 10.The communication method according to claim 9, wherein the firsttransmission power for the first uplink signal is prioritized over thesecond transmission power for the second uplink signal.
 11. Thecommunication method according to claim 9, wherein the firsttransmission power for the first uplink signal is reserved in a casewhere the first uplink signal is prioritized over the second uplinksignal.
 12. The communication method according to claim 9, wherein thesecond transmission time interval is within the first transmission timeinterval.
 13. The communication method according to claim 9, wherein thefirst transmission time interval is one subframe, and the secondtransmission time interval is shorter than one subframe.
 14. Thecommunication method according to claim 9, wherein the first RAT is along term evolution (LTE), and the second RAT is a new RAT.
 15. Thecommunication method according to claim 9, wherein a subcarrier spacingin the first RAT is narrower than a subcarrier spacing in the secondRAT.
 16. The communication method according to claim 9, wherein asubcarrier spacing in the first RAT is 15 kHz, and a subcarrier spacingin the second RAT is 60 kHz.